Material Properties Of Specimens Research Articles

Evaluation and consideration of local specimen material properties in lifetime prediction of short fiber‐reinforced PA6T/6I

AbstractTo exploit the full material potential of short fiber‐reinforced PA6T/6I, specific component calculations including anisotropic material behavior is necessary. For this, different failure criteria and fatigue models are used to describe the behavior during a component service life. This paper deals with the determination and consideration of fiber orientations (FOs) for failure criteria and fatigue calculations. Therefore, a novel method to determine FO distributions across injection‐molded plates is proposed. The developed method allows a forecast of FOs for different specimen extraction positions and angles on injection‐molded plates by using only a few measured reference points. As a result, fatigue models can be calibrated with the strength values and the corresponding FO, calculated for fracture position. The performed tests show a non‐negligible influence of failure positions, due to FO distributions along the specimens. So, the FO determination method delivers an improvement in strength values estimation.

Experimental investigation on cold-formed steel lipped channel beams affected by local-distortional interaction under non-uniform bending

This paper reports an experimental investigation, carried out at The University of Hong Kong, on the behaviour of cold-formed steel lipped channel beams affected by local-distortional (L-D) interaction under non-uniform bending – to the authors’ best knowledge, these are the first tests specifically devoted to this topic. This investigation consists of 16 non-conventional four-point simply supported bending tests involving twin lipped channel beams arranged in a “back-to-back” configuration and laterally restrained at the loading points. The 32 lipped channel specimens were brake-pressed from high-strength zinc-coated G450 grade structural steel sheets. Tensile coupon tests were performed to obtain the specimen material properties and initial geometrical imperfections were measured prior to testing. The beam geometries were carefully selected to enable testing beams that are prone to “true L-D interaction” (close critical distortional-to-local buckling moments) when acted by trapezoidal bending moment diagrams with four distinct gradients – all the tested specimens exhibited the sought L-D interactive nature. The output of the experimental investigation consists of (i) applied moment vs. displacement equilibrium paths, (ii) photos showing beam deformed configurations along those paths (including the failure modes) and (iii) the failure moment data. Lastly, the experimental failure moments obtained are compared with their predictions provided by the (i) current local and distortional Direct Strength Method (DSM) strength curves and (ii) available DSM-based approaches against L-D interactive failures, which were developed and calibrated exclusively in the context of beams subjected to uniform bending.

Experimental investigation on cold-formed steel stiffened lipped channel columns undergoing local-distortional interaction

Abstract The objective of this work is to report a careful experimental investigation, planned at the University of Lisbon and carried out at The University of Hong Kong, concerning the behaviour and ultimate strength of cold-formed steel web-flange-stiffened (WFSLC) and web-stiffened (WSLC) lipped channel columns undergoing local-distortional (L-D) interaction. It involves 31 specimens (16 WFSLC+ 15 WSLC), brake-pressed from high-strength zinc-coated grades G450, G500 and G550 structural steel sheets, exhibiting critical distortional-to-local buckling load ratios ranging between 0.75 and 1.88. The column geometries were carefully selected to enable testing fixed-ended columns undergoing true L-D interaction and secondary distortional-bifurcation L-D interaction (ensuring evidence of the latter required selecting rather slender columns) − all tested specimens exhibited the expected L-D interactive failures. The specimen material properties were obtained from tensile coupon tests and their initial geometrical imperfections were measured prior to testing. The experimental results presented and discussed consist of column (i) load-displacement equilibrium paths, (ii) photos evidencing the evolution of the column deformed configurations along those paths (including the failure mode) and (iii) failure loads. Finally, the experimental failure load data obtained are compared with their estimates provided by the currently codified DSM design approaches for columns failing in L and D modes, showing their inadequacy to handle L-D interactive failures − the fresh light shed by this comparison will contribute to the timely codification, in the near future, of a DSM design procedure for columns affected by L-D interaction.

Tribological properties of the vane head / stator of hydraulic vane motor in the low ambient temperature

Deck machinery that is driven by hydraulic motor is a key part for ship exploration in polar area. The reliability of hydraulic motor which works as the key power source of deck machinery is concerned by manufacturers, especially under very low temperature. The low temperature friction characteristics is one of the important factors that influence the reliability of the motor. In this paper, the hydraulic vane motor in deck machinery was taken as the research object. The friction test of the vane head which was made of polyimide (SP21, E.I.Du Pont Company) and the stator, which is made of nodular cast iron(brand is QT350-22L, ISO 1083:2004), was carried out by using the low-temperature tribology tester. Wear tests were performed using a pin-on-disc structure under five different temperatures (−10 °C,-20 °C,-30 °C,-40 °C and −50 °C) and three different loads (300N, 450N and 600N) respectively. In order to analyze the wear mechanism of the friction test specimen under different condition, the surface morphology figures of specimen were got by digital microscope system (DMS). The experiment results showed temperature and load have a great influence to the friction coefficient. With temperature decreasing, the friction coefficient does not change linearly, because the mechanical properties of specimen material and the lubrication medium varied significantly in low temperature. Moreover, typical wear and tear patterns are different in different working temperatures. Therefore, the failure mechanism of the hydraulic motor was summarized. The research can not only optimize the design of hydraulic motor, but also provide reference data for the establishment of online intelligent fault diagnosis system of marine deck machinery.

Numerical Simulation on the specimen dynamic plastic deformation behaviour in the torsional split Hopkinson bar test

The torsional split Hopkinson bar (SHB) is an important method to study the dynamic shear behaviour and shear localization of materials under high strain rates. Different specimen sizes were used in literatures, and the size of the specimen might have an effect on the experimental results. Numerical simulation on torsional SHB tests was carried out with LS-DYNA. The strain signal on the incident and transmitted bars were obtained from the simulation just as the experiment. Then the numerical strain-stress relationship of the material was derived from the numerical strain signal using the experiments data process of torsional SHB. The agreement between numerically derived strain-stress results and the specimen material properties specified in numerical modelling indicates that the torsional SHB is applicable to study the dynamic shear behaviour of materials under high strain rates. The specimen gauge diameter has no significant effect on the dynamic torsional test result. However, higher adhesive strength is required to fix the larger gauge diameter specimen on the bars. The specimen gauge thickness has little effect on the experimental results with a modified formula to calculate the specimen stress. Still, the increase of specimen gauge thickness will lead to the increase of non-uniformity of specimen stress and strain (strain rate). Based on the simulation analysis, suggestions on the specimen size design are given as well.

Determination of the material properties of polymers using laser-generated broadband ultrasound

Abstract. In the non-destructive determination of material properties, the utilization of ultrasound has proven to be a viable tool. In the presented paper, a laser is used to create broadband acoustic waves in plate-shaped specimens by applying the photoacoustic effect. The waves are detected using a purpose-built ultrasonic transducer that is based on piezoceramics instead of the commonly used piezoelectric polymer films. This new transducer concept allows for detection of ultrasonic waves up to 10 MHz with high sensitivity, thereby allowing the characterization of highly damping materials such as polymers. The recorded data are analysed using different methods to obtain information on the propagation modes transmitted along the specimen. In an inverse procedure, the gained results are compared to simulations, yielding approximations for the specimen's material properties.

Usage of the concept of the effectively shaped indenter for the determination of yield stress from Berkovich nano-indentation experiments

Abstract Determining the yield stress Y in addition to the indentation modulus E I T and hardness H I T from Berkovich nano-indentation experiments would widely open up their possible uses. Because of their self-similarity there is not enough information obtainable from such experiments to characterize the complete stress-strain curve of the specimen. Nevertheless it could be shown by Schwarzer and Pharr (2004) that for some selected materials the concept of the effectively shaped indenter (CEI) seems to provide good results when used to determine the yield stress Y from Berkovich indentations. However, further research providing a more complete overview why and under which circumstances the CEI is able to give such adequate results for the yield stresses is still missing. In this work, a wide spread database of simulated and experimental Berkovich nano-indentation force-displacement curves together with reference values for the yield stresses was utilized. Applying the CEI to these force-displacement curves revealed how the specimen material properties affect the usability of the CEI (Fig. 3). To give a better understanding of these phenomenological findings, an explanation of the behavior of the CEI based on the physics of the involved contact situations is given. The results lead to the conclusion that the spatial maxima of the von Mises stress delivered by the CEI do not generally represent the yield stress but rather refer to the indentation hardness H I T . This is due to the fact that the stress-strain field, especially the hydrostatic part, within the yield zone is not properly reflected by the elastic CEI model.

A variable-width harmonic probe for multifrequency atomic force microscopy

In multifrequency atomic force microscopy (AFM) to simultaneously measure topography and material properties of specimens, it is highly desirable that the higher order resonance frequencies of the cantilever probe are assigned to be integer harmonics of the excitation frequency. The harmonic resonances are essential for significant enhancement of the probe's response at the specified harmonic frequencies. In this letter, a structural optimization technique is employed to design cantilever probes so that the ratios between one or more higher order resonance frequencies and the fundamental natural frequency are ensured to be equal to specified integers and, in the meantime, that the fundamental natural frequency is maximized. Width profile of the cantilever probe is the design variable in optimization. Thereafter, the probes were prepared by modifying a commercial probe through the focused ion beam (FIB) milling. The resonance frequencies of the FIB fabricated probes were measured with an AFM. Results of the measurement show that the optimal design of probe is as effective as design prediction.

The influence of accelerated curing on the properties used in the prediction of chloride ingress in concrete using a Nernst–Planck approach

This paper examines the use of accelerated aging as an expedited method to determine the material property inputs for service life modeling. When the samples are cured in saturated lime water, it is noticed that accelerated aged specimens at 50±2°C consistently showed higher porosity, a greater chloride diffusion coefficient, and greater permeability. Service life predictions modeled using material properties of specimens when aging was accelerated could result in the prediction of corrosion initiation at a time that was up to 30% earlier than using properties of conventionally cured specimens at the same equivalent age.

Ultimate Behavior of GFRP Shell Structure Stiffened by Steel Pipe Ring

The experiment and FE analysis of ultimate behavior of GFRP cylindrical shell structure stiffened by steel pipe ring instead of rectangular cross-section ring was presented. Four kinds of test models were designed and flexural failure experiment was performed to investigate ultimate behavior characteristic according to the size of cross section of steel pipe ring and diameter of GFRP shell. Material properties of specimens were experimented by bending, tensile and compressive test. Displacements and strains were measured to evaluate failure behavior of steel pipe ring and GFRP shell structure. The experimental results were compared with the FEA results by commercial program ABAQUS. It is observed that GFRP shell structure stiffened by steel ring have enough ductility to bending failure, and an increase of bending rigidity of steel ring is very effective to increase of failure strength of GFRP shell structure.

Interlaminar Fracture Testing Method for CFRP Using Tensile Loading with Acoustic Emission Analysis

A method is described to characterize the uniformity of interlaminar fracture toughness of laminated carbon-fiber-reinforced polymer (CFRP) composites fabricated by the modified vacuum assisted resin transfer molding process. To prepare specimens for Mode I fracture toughness tests, pieces were sectioned from the inlet and vent regions of a CFRP plate ([+30/-30]6), with a starter crack inserted. The specimens were packed between two rectangular epoxy plates to apply a load using a universal testing machine. Acoustic energy signals were monitored using two sensors attached to the epoxy plates during tensile loading. The difference between the material properties of specimens from the inlet and vent regions of the CFRP plate were statistically compared using one-way analysis of variance (ANOVA); we show that the specimens showed no statistically significant differences in the interlaminar fracture characteristics depending on the part of the mold from which they were taken.

Sensitivity of resistive and Hall measurements to local inhomogeneities

We derive exact, analytic expressions for the sensitivity of resistive and Hall measurements to local inhomogeneities in a specimen's material properties in the combined linear limit of a weak perturbation over an infinitesimal area in a small magnetic field. We apply these expressions both to four-point probe measurements on an infinite plane and to symmetric, circular van der Pauw discs, obtaining functions consistent with published results. These new expressions speed up calculation of the sensitivity for a specimen of arbitrary shape to little more than the solution of two Laplace equation boundary-value problems of the order of N3 calculations, rather than N2 problems of total order N5, and in a few cases produces an analytic expression for the sensitivity. These functions provide an intuitive, visual explanation of how, for example, measurements can predict the wrong carrier type in n-type ZnO.

Assessment of Heat Treated Inconel X-750 Alloy by Nonlinear Ultrasonics

The nonlinear ultrasonic technique is known as a promising tool for monitoring material states related with micro-structural changes, with improved sensitivity compared to conventional nondestructive testing techniques. It is well known that degradation of material properties is generally accompanied by the increase of material nonlinearity. However, the trend has been rarely investigated in the opposite way for improved material properties. In this paper, nonlinear ultrasonic waves are used to assess the material condition of heat treated Inconel X-750 alloy based on the nonlinear acoustic parameters. Material property testing is conducted to compare the influence of heat treatment for comparison with the nonlinear parameter based prediction. The material properties of specimens are improved by applying heat treatment, with significant decreases in the acoustic nonlinearity. The better the mechanical property achieves via heat treatment, the smaller the acoustic nonlinearity becomes. It can be concluded that the nonlinear acoustic technique can be used to evaluate the effect of heat treatment nondestructively, and to optimize the process, thus providing another indication of the feasibility of using the nonlinear ultrasonic technique for material characterization.

Experimental Study on the Durability of Glass Fiber Reinforced Polymer Pole and Tower for Power Transmission

This paper studied the durability of Glass Fiber Reinforced Polymer (GFRP) Pole and Tower for power transmission under the UV and adverse temperature environment. The results show that both UV and adverse temperature environment influence the performance of GFRP material, with its strength significantly reduced, and its elastic modulus increased, while the Poisson's ratio changed slightly. Xenon lamp aging affects the material properties of the specimens with protective coatings more slightly than those without any protective coatings. High temperature environment affects the material properties of specimens more obviously than low temperature environment does. Therefore, when designing the GFRP Pole and Tower for power transmission exposed in UV and adverse temperature environment long-term, designers should consider the negative impacts of the external environment, and take appropriate protective treatments.

The sharpness of a Berkovich indenter

Precise calibration of the indenter shape is an important procedure in nanoindentation analysis since the indenter geometry enters directly into the most common methods of data analysis in this type of testing. Not only is the geometry required to be known with some precision, but also the sharpness of the tip, especially in the case of pyramidal indenters, is important for the use of indenters for testing hardness in thin film specimens—the most common application of nanoindentation. In this paper, a method of determining the area function and tip radius for a Berkovich indenter is described. It is shown that the tip radius estimated from the area function data is in reasonable agreement with a direct measurement using a calibrated atomic force microscope. It is shown that subjective decisions about tip radius may lead to unjustified rejection of a tip for hardness measurement. A new criterion for tip quality is presented in terms of tip radius and specimen material properties.

Stress field of orthotropic cylinder subjected to axial compression

Based on the constancy hypothesis of material volume, the circumferential and radial stresses of a cylinder specimen are analyzed when the cylinder is subject to a loading along the axial direction. The circumferential and radial stress distribution is a power function of radius parameter when the constitutive relation of specimen material is orthotropic. The stress distribution is a quadratic function of radius parameter for transversely isotropic material. Along the cylinder axial line, the circumferential and radial stresses are maximum and equal to each other. In the circumference boundary surface, the radial stress is zero and the circumferential stress value is minimal. The failure theory of maximum tensile circumferential strain is applied to calculate the critical axial loading. The circumference-boundary-layer failure criterion of orthotropic cylinders is described with the Hill-Tsai strength theory. The obtained strength theory is related to axial stress and mechanical properties of specimen material and to the specimen axial-deformation strain rate and the change rate of strain rate.

Numerical simulation of impact on pneumatic DTH hammer percussive drilling

The process of DTH (down-the-hole) hammer drilling has been characterized as a very complex phenomenon due to its high nonlinearity, large deformation and damage behaviors. Taking brittle materials (concrete, granite and sandstone) as impact specimens, the explicit time integration nonlinear finite element code LS-DYNA was employed to analyze the impact process and the penetration boundary conditions of DTH hammer percussive drilling system. Compared with previous studies, the present model contains several new features. One is that the 3D effects of DTH hammer drilling system were considered. Another important feature is that it took the coupling effects of brittle materials into account to the bit-specimen boundary of the drilling system. This distinguishes it from the traditional approaches to the bit-rock intersection, in which nonlinear spring models are usually imposed. The impact forces, bit insert penetrations and force-penetration curves of concrete, granite and sandstone under DTH hammer impact have been recorded; the formation of craters and fractures has been also investigated. The impact loads of piston-bit interaction appear to be relatively sensitive to piston impact velocity. The impact between piston-bit interaction occurs at two times larger forces, whereas the duration of the first impact doesn’t change with respect to the piston velocity. The material properties of impact specimen do not affect the first impact process between the piston and bit. However, the period between the two impacts and the magnitudes of the second impact forces greatly depend on the specimen material properties. It is found that the penetration depth of specimen is dependent on the impact force magnitude and the macro-mechanical properties of the brittle materials.

Large-Scale Processing of Engineered Cementitious Composites

Large scale investigation of engineered cementitious composite (ECC) design, processing, and evaluation is undertaken up to 3 cu m (4 cu yd). In order to retain high-performance fiber-reinforced cementitious composites (HPFRCC) characteristic pseudo-tensile strain-hardening properties while transit truck mixing procedures and short mixing times are optimized, ECC design is undertaken. Tensile multiple cracking and grain size distribution criterion form the basis of material design. Both large scale (3 cu m (4 cu yd) and small scale (200 L (7 cu ft)) design procedure success is demonstrated. To establish a preliminary large-scale mixing test result statistical analysis-based preliminary design value set, there was testing of large-scale mixing specimen material properties. Tests show that for the ECC-M45 material tested with 99% confidence, tensile strain, tensile strength, and compressive strength design parameters can be set at 2.0%, 4.35 MPa (630 psi), and 60 MPa (8.75 ksi), respectively.

The effect of the monomer-to-powder ratio on the material properties of acrylic bone cement.

The procedure percutaneous vertebroplasty consists of injecting polymethylmethacrylate cement into vertebral bodies for the treatment of osteoporotic compression fractures and tumors of the spine. Clinicians practicing vertebroplasty commonly alter the mixture of monomer-to-powder recommended by the manufacturer in an effort to decrease viscosity and increase the working time. The purpose of the current study was to measure the effect of varying the monomer-to-powder ratio on the compressive material properties (compressive modulus, yield stress, and ultimate compressive strength) of the cement Simplex P (Stryker-Howmedica-Osteonics, Rutherford, NJ). Cylindrical specimens were prepared using monomer-to-powder ratios of 0.45 to 1.00 mL/g and tested in compression. Peak compressive material properties occurred at the mixture ratio recommended by the manufacturer (0.5 mL/g) but decreased as the ratio of monomer to powder was increased. The material properties of specimens cured for 1 hour were significantly less than those for specimens cured for 24 hours. The monomer-to-powder ratio affects the compressive material properties of cement. The clinical significance of these results with respect to vertebroplasty is yet to be determined.

Determination of coating mechanical properties using spherical indenters

In recent years, various forms of indentation testing have been increasingly used to determine the material properties of specimens. This technique, particularly the nano-indentation method, has been extended to the testing of coating systems in order to calculate the individual properties of the thin coatings and the substrates. However, the interpretation of the test data to achieve this is complex and continues to be a widely studied subject. Based on the finite element analysis (FEA) of coated surfaces indented by a spherical indenter, this paper describes methods for combining FEA and experimental indentation testing to determine coating modulus and hardness independent of substrate effects. An indentation test on a coated specimen is first carried out using a spherical indenter. The combined contact modulus of the coated surface is determined from the elastic portion of the experimental load/displacement curve. The modulus of the coating alone is then computed from a function derived by a parametric finite element analysis of indentation behaviour. The hardness of the coating alone is determined by comparing the experimentally determined mean contact pressure with parametric finite element results for the same contact geometry and known hardness ratios. Using this proposed methodology, the properties of the substrate are fully taken into consideration, hence providing a more universal and accurate measurement of coating elastic modulus and hardness.